The long-term goal of the proposed research is to investigate the relative roles of cell-mediated and humoral immunity in resistance to reinfection in experimental murine crytococcosis. A model of cryptococcosis will be developed in normal (immunologically unmodified) mice, and the model will be used to evaluate immunity in thymectomized mice, the latter of which will be thymectomized as adults, lethally irradiated and reconstituted with syngeneic bone marrow cells. Attempts will be made to correlate the temporal development of delayed hypersensitivity or antibody with resistance to reinfection, resistance being measured by intravenous challenge at selected intervals following cutaneous inoculation with viable cryptococci. In vitro measures of cell-mediated immunity will be evaluated by lymphocyte stimulation and assay for migration inhibition factor. CBA/J mice a syngeneic strain, will be used throughout the studies and attempts will be made to passively transfer delayed hypersensitivity and resistance to reinfection to normal and thymectomized mice using cells or serum from normal "immune" donors. If such attempts are successful with cells, attempts will be made to abrogate the transfer by prior treatment of the cells with anti-theta serum. New test materials will be developed in conjunction with these studies for possible use as antigens in humoral and cell-mediated assays.